In the ongoing effort to improve tire design, there is a recognized tension among tire performance, rolling resistance (or fuel economy), and treadwear. Typically, for use in a consumer tire, a tread compound is designed to optimized between these three considerations. However, efforts to improve for example fuel economy often lead to compromises in performance and/or treadwear. For higher performance tires desired by driving enthusiasts, the achievement better performance often comes with a compromise in treadwear or fuel economy. There is a desire therefore to develop tread compounds that can achieve improvement in any of performance, fuel economy, and treadwear with little or no compromise in the other two. One approach is in the elastomeric polymers used in the tread compound.
The reversible addition-fragmentation chain transfer (RAFT) polymerization is a versatile controlled radical polymerization method which can be used for the polymerization of a variety of monomers. Due to the controlled characteristics of the RAFT-polymerization, the polydispersities of the resulting polymers are relatively low and their molecular weights can be modified within a wide range by changing the initiator and CTA concentration. The RAFT-polymerization is initiated by a radical starter (for example AIBN) and a chain transfer agent (CTA). Suitable CTAs contain thiocarbonylthio-moieties such as dithioesters, trithiocarbonates, dithiocarbamates and xanthates. After the RAFT-polymerization, the respective thiocarbonylthio-moieties remain attached to the polymer chains as functional endgroups.